1. Field of the Invention
The present invention relates to agents for the pulp and/or surface sizing of paper, which comprise aqueous, solventless dispersions of cationic polymers. The present invention further relates to a process for sizing paper by using said agents.
2. Discussion of the Background
In the production of ink resistant and printing papers the papers are sized at the surface or in the pulp; this is to decrease the wettability of cellulose and the absorption of water or aqueous liquids through the capillary system of the sheet, and to improve the absorption of printing inks, the whiteness and opacity as well as the mechanical properties of the paper sheet. The known sizing process and the agents normally used are described in Ullmanns encyclopedia, volume 17 (1979), pages 585-587 and 599.
It is also known to use cationic polymers in the sizing process, they stand out for a high substantivity towards cellulose fibers. Japanese Patent No. J 04 108 196 describes cationic sizing agents based on colophony and cationic polymers. Japanese Patent Nos. J 04 091 290, J 63 270 893, and J 59 159 198 describe sizing agents formed of dimeric alkylketenes and cationic polymers.
DE 37 37 615 C2 describes sizing agents representing resins modified with carboxylic acid, so-called fortified resins which are dispersed by portions of cationic copolymers. In this connection the cationic copolymers are obtained by polymerization in solution, and the production of the dispersed sizing agent from the anionically modified resins and the cationic copolymers is effected in a complicated method by removing the solvent from the copolymer by means of distillation, melting the modified resin, and dispersing in water, in some cases using surfactants. During application, the resin components not bound in the pulp load the process water and must be removed, if necessary by using additional auxiliaries.
DE 38 26 825 C2 describes cationic sizing agents that are formed from methyl (meth)acrylate, butyl (meth)acrylate, acrylic acid, and 10-30 percent by weight of portions of N,N-dimethylaminoethyl(meth)acrylate, and which comprise isopropanol or other organic solvents. The described sizing agents are unstable during storage and insufficiently active when applied.
EP 416 427 B1 describes sizing agents based on aqueous, cationic polymer dispersions whose polymer portion is formed of only 2-20%-wt. of a salt-forming, water-soluble monomer having groups of alkyl ammonium, alkyl sulfonium, or alkyl phosphonium, but which are always used with additional cationic polymers, such as retention agents and protective colloids (Poly-DADMAC). For this reason these polymers must nevertheless be used in larger amounts. Additionally, the described dispersions also comprise emulsifiers and, in particular, nonionic surfactants which--in addition to the water-soluble retention agents in the paper--may impair the sizing action and load the industrial process water.